Keyboard percussion instruments, such as vibraphones and marimbas, are musical instruments that have tone bars and are played upon by musicians with mallets. Keyboard percussion instruments of the type played on by hand-held mallets fall into two distinct categories. non-resonator instruments such as the glockenspiel (orchestra bells) and chimes (tubular bells); and resonated instruments such as the marimba, xylophone and vibraphone (“vibes”).
Resonated instruments such as the vibraphone have resonators, usually a tube, acoustically coupled with a tone bar. The resonators of keyboard percussion instruments serve to amplify the sound of the tone bar above. Instruments of this genre that have long ringing aluminum or steel bars, such as the vibraphone and glockenspiel, often have a dampening system to allow the player to control the ring time of the bar, usually through the operation of a foot pedal. This pedal operates similarly to the sustain pedal of a piano. Pressing the pedal removes the damper bar from the keyboard; releasing the pedal allows it to return to its former dampening position, usually by means of a spring mechanism.
The vibraphone frequently has one feature which is unique to it, and which is the basis for its name, which is a spinning pulsar disk in a resonator tube. A diagram of this is shown in FIG. 1. Positioned in the upper portion of a resonator tube 101 in FIG. 1 is a set of rotating or spinning pulsar/fans 102 in FIG. 1 is an example, mounted on an axle or pulsar fan shaft 103, powered by an electric motor 104. These spinning disks open and close the top opening of the resonators, producing the distinctive steady vibrato sound. In the existing version of the vibraphone, the vibrato strength varies steadily with each rotation of the disks inside the resonators, from substantially closed tubes, with the pulsar disks in the horizontal position, as shown in FIG. 2a, with the pulsar disk moving to an intermediate position as shown in FIG. 2b, and with the pulsar disk in the substantially open position as shown in FIG. 2c. Some efforts are known to attempt to provide control to a musician to stop disks at a pre-set angle. For instance, U.S. Pat. No. 4,619,178, issued on Oct. 28, 1986 and entitled Stop Angle Controller for a Vibrato Mechanism on a Vibraphone, discloses an electronic system for setting a stop angle for a pulsar disk.
In the existing version of the vibraphone, the speed of the vibrato may be controlled by adjusting the rotation of the electric motor, but with almost no possibility for the player to precisely control the vibrato speed to match the underlying rhythm of the music or to adjust the speed on an instantaneous basis to match the expressive needs of an individual note, chord or moment in the music.
Existing vibrato mechanisms have some additional significant shortcomings. In all forms of the existing vibrato mechanism used in keyboard percussion instruments, the mechanism that produces the vibrato effect blocks a substantial portion of the resonance of the tube. This is because the pulsar fans and the shaft on which they are mounted are both located within the resonator itself. Even in the full open position, half of the pulsar fan is down in the tube and the other half of it is directly above the tube, partially blocking the acoustics of the tube from the tone bar.
In this open position, where maximum resonance is desirable, the pulsar disks and shaft interfere with the sympathetic resonance of the tone bar and tube, the coupling of which is the essence of the sound of resonated keyboard percussion instruments. The existing art has a further disadvantage: In the closed position, the resonator is never really closed off from the tone bar because of the clearance necessary between the circumference of the pulsar disks and the inside diameter of the tubes. In this closed position there is always leakage around the pulsar disk into the resonator.
Thus, even in well made, carefully engineered instruments, the existing method of producing vibrato never produces the full potential range of vibrato. It never reaches full potential maximum volume when open, nor potential minimal volume when closed.
If the disk and tube were engineered to closely mate in size so as to minimize leakage around the disk, any slight misalignment of any of the thirty-seven (37) disks on a 3-octave instrument would produce unacceptable noise levels. It is a well-known problem with keyboard percussion instruments that even in loosely mated designs, the spinning disks and shaft are often too noisy to use in soft musical passages. Thus, in the precise musical environment where vibrato would be most appropriate (soft ballads and other sustained musical styles), the noisy, existing methods of producing vibrato make it impossible for the musician to consider. Turning the electric motor on frequently results in the sound of a decidedly unmusical chatter of clicking and spinning of fans in tubes.
Another disadvantage of the existing methods of producing vibrato is that the upper open ends of the resonator tubes (nearest to the tone bars) must be notched out or otherwise deformed to accommodate the pulsar fan shaft. See for instance notch 300 in FIGS. 2a-2c as an illustration of this. This notching of the tubes weakens the resonance, adds undesirable non-harmonic overtones to the remaining resonance and detunes the resonator's frequency from the natural tone that would be obtained by a tube that had an unaltered cylindrical shape
The full vibrato effect (100% resonated volume to 0% resonated volume and back to 100%) has never been achieved through prior art because the pulsar fan assembly never fully closes the resonator, nor allows for a fully resonated tone. The existing methods are also inherently noisy since they involve power provided by an electric motor that spins a long assembly of disks inside of the resonators. As a result of these well-known shortcomings, vibraphones are often ordered without the “vibes” (that is: without the motor and pulsar disk assembly).
In recent years, improvements have been made to the pulsar fan mechanism of vibraphones. These improvements were mostly of a mechanical nature: attempting to make the motor run more quietly through the use of higher-quality bearings on the pulsar fan shaft; the use of timing belts (rather than simple pulleys) to keep the two sets of pulsar disks phase-aligned (the pulsar disks in the sharp and natural resonator tubes are open and closed in phase with one another); devices to assure that the pulsars stop rotating in the open position when the motor is turned off; etc. However, all of these developments have been refinements of the same motor-driven mechanism that has been manufactured worldwide for more than 70 years and they do not address the inherent weaknesses of the system.
Another weakness of the current motor-driven vibrato system is the interface between the player and the vibrato mechanism. The sound of a vibraphone (or similarly-equipped marimba or other keyboard percussion instrument), when the pulsar disks are spinning powered by an electrical motor, is comprised of a steady-speed, mechanical, non-expressive vibrato that does not respond instantaneously to the musical desires of the player. The motor can be sped up or slowed down by manipulating the controls, but matching a particular rhythm, or enhancing individual notes within a phrase in a controlled manner is impossible, even with existing recent interfaces between player and electric motor. Even if the motor speed could be set with metronome-like precision, it would not follow the moment-to-moment bending of tempo, which is common in musical performance, nor could it respond to the creative whims of a jazz musician. It should be appreciated by one of ordinary skill in the art that the current electro-mechanical method of controlling the speed of vibrato is primitive and it lacks the refined speed control available to other instrumentalists or vocalists.
Vibrato has the dimension or quality of “depth” or “strength” in addition to the more obvious dimension of speed. With respect to keyboard percussion instruments, the perception of “depth” of vibrato is directly related to the volume or strength of resonance of the tone bar and tube. Current art does not permit variations of strength of vibrato. As the pulsar fans rotate on the shaft at the set speed of the motor, the strength or “depth” of the resonance varies in exactly the same way with each rotation—vertical/open followed by horizontal/closed. The volume levels achieved by the present rotational method are approximately 85-90% of maximum resonance when open, down to approximately 10-15% of the minimum resonance when closed. There is no possibility for the musician to even contemplate a vibrato comprised of 70% open/25% open and 70% open/25% open, or to progressively cycle through a musical crescendo of, for example, 5% open/10% open, 5% open/20% open, 5% open/40% open and so forth. There are a myriad of musical possibilities and applications for varying the depth of vibrato, and all are beyond the capabilities of the current art of keyboard percussion vibrato.
In contrast to the tone of the vibraphone, the vibrato of any string instrument or the human voice modulates in speed and depth according to the expressive musical desires of the performer. Sometimes the vibrato gets faster or slower as a note is sustained, sometimes it is completely absent in the beginning of a note and then gradually added toward the end, as is often heard on held notes in popular ballade singing. The vibraphone or any keyboard percussion instrument in its present form is incapable of any such musical expression because of the awkward interface of performer and motor and the unvarying repetitive, rotational nature of the method of producing the vibrato. These basic musical deficiencies are why the vibraphone is described as “cool and detached” to most listeners, rather than “warm and expressive”.
In recent years some improvements have been attempted to the interface of the player with the motor. While most professional quality vibraphones have an adjustable speed motor, the adjustment is imprecise and requires the performer to adjust the controls of the motor while commonly holding four mallets: two in each hand. One such attempted improvement gives the musician the ability to turn the motor on or off using a single strike of the mallet. Another attempted improvement allows the player to pre-set two speeds of the motor, either of which can be selected by the player with a single strike of the mallet or by passing the hand through the beam of a photo-electric switch. In either of these cases however, the speed of the motor, once started, is not linked in any way to the background rhythm or tempo of the music, nor is it responsive to the ebb and flow of the tension and release of individual notes, chords and passages. In one early design of the vibraphone, a button was mounted on the damper pedal, the purpose of which was limited to temporarily speeding up the motor to its maximum for a momentary fluttering special effect.
In each of these cases, the attempted improvement in the interface does not even contemplate note-to-note, moment-to-moment real time control of the speed or depth of the vibrato. However, anything short of complete control leaves the keyboard percussionist's control of vibrato in the realm of a “special effect” rather than elevating vibrato to an integral part of the creative process of making music, as it already is with the human voice or any string, woodwind and brass instrument.
Accordingly, it would be desirable to provide new methods and apparatus for creating vibrato in keyboard percussion instruments and the instrument-musician interface.